1. The Field of the Invention
The present invention relates generally to vehicle transmissions. More particularly, it concerns a variable-ratio transmission device.
2. The Background Art
Transmission devices are well known in the field of motorized vehicles for converting and transmitting the force generated by an engine to an output shaft. It is known to make efficient use of the motor power by adjusting the gear ratio between the input and output shafts responsive to variation in loads on the output shaft, or on the input shaft. For example, a higher gear ratio often provides a more efficient transfer of force for larger loads on the output shaft. Conversely, a lower gear ratio often suffices for lesser loads on the output shaft.
The need to optimize the motor power by varying the gear ratio has motivated the development of many different transmission devices capable of shifting between gear ratios. The standard transmission is known in the field to permit an operator to shift between various gear ratios by operating a hand-shift lever in conjunction with a foot clutch. Automatic transmissions have been developed which accomplish an automatic shifting between gear ratios responsive to increases and decreases in load on the output shaft.
Another approach to vehicle transmissions is the concept of a continuously variable transmission, which automakers have attempted for years to develop. It is thought that energy transfer between the motor and the output shaft can be further optimized by providing an infinite range of gear ratios between the minimum and maximum gear ratios, instead of merely four or five different gear ratios. This idea is a good one, since variation in load on the output shaft tends to increase and decrease gradually and continuously. Indeed, it stands to reason that provision of an optimal gear ratio for each and every load variation on the output shaft would maximize the efficiency of the vehicle. However, there have been many practical difficulties with the prior art transmission devices which offer continuously variable gear ratios.
There is thus a need for a variable-ratio transmission which is simple in design, manufacture and operation.